I create RAID10 using "mdadm --create ... --metadata=0.90 ...". There are four partitions which I name from /dev/md128 to /dev/md131. First thing strange is that mdadm automatically changes them from /dev/md120 to /dev/md123, why?

"cat /proc/mdstat" and "mdadm --detail --scan" seem normal. I meet some trouble doing "grub-install /dev/sda", which reported disk "/dev/md120" not detected . There are lots of discussions regarding this problem but no very clear solution. I end up manually modifying /boot/grub/device.map with a new line "(md120) /dev/md120", then grub-install goes through with no error reported.

When booting, after passing the machine logo, the next window shows RAID volumes: not detected, followed by the information of four hard drives (marked as not raid disk). Then error: no such device plus a long key (like uuid). Then "grub rescue >".

In grub rescue, I try "ls" but "(md120)" is not there. Apparently, the RAID is not recognized properly and previous "grub-install" is a fake success.

Already spent a few hours, so what goes wrong and how to fix it? Thanks a lot, really appreciated.

BTW, I install RAID using system rescue cd and then chroot. The boot partition is imaged from another similar system. The content looks fine when I check. Anyway, I feel it shouldn't matter because RAID is not detected in the first place.